This invention relates to a digital printing system. More particularly, the invention relates to a digital printing system for printing on both surfaces of a sheet of print media.
According to the invention, there is provided a digital printing system for printing on both surfaces of a sheet of print media, the printing system including:
a first print engine; and
a second print engine in an opposed, aligned relationship with the first print engine, each print engine including an inkjet printhead and a transfer roller on to which ink ejected from the printhead is deposited to be applied, in turn, on an associated surface of the print media, the transfer roller of one print engine further serving as an urging means for the transfer roller of the other print engine for urging the transfer rollers into contact with their associated surfaces of the print media.
The second print engine may be pivotally mounted with respect to the first print engine, the second print engine including a biasing means, in the form of a spring, for biasing its transfer roller into abutment with the transfer roller of the first print engine. Thus, it will be appreciated that the transfer roller of each print engine serves as a pinch roller for its opposed print engine.
One of the transfer rollers of both transfer rollers may act as an urging means for urging the sheet of print media past the transfer rollers.
At least a surface of the transfer roller of each print engine may be of a wear resistant material which is resistant to pitting, scratching or scoring. The material may be titanium nitride.
Each print engine may include a page width printhead with the transfer roller being of a similar length to the printhead.
In this specification, unless the context clearly indicates otherwise, the term xe2x80x9cpage width printheadxe2x80x9d is to be understood as a printhead having a printing zone that prints one line at a time on a page, the line being parallel either to a longer edge or a shorter edge of the page. The line is printed as a whole as the page moves past the printhead and the printhead is stationary, i.e. it does not raster.
The printhead of each print engine may include an ink-ejecting means and a sealing means surrounding the ink-ejecting means. The ink-ejecting means of the printhead may be a microelectromechanical device having a plurality of inkjet nozzles.
The sealing means may be an elastomeric seal surrounding the ink-ejecting means.
When the printhead of each print engine is inoperative, it may bear against its associated transfer roller such that the sealing means seals the ink-ejecting means to inhibit evaporation of ink from the ink-ejecting means, each print engine including a displacement means for withdrawing the printhead from the transfer roller when printing is to be effected.
The displacement means may include an electromagnetically operable device. The electromagnetically operable device may be a solenoid which, to draw the printhead away from the transfer roller to enable printing to be effected, requires a first, higher current, and to hold the printhead in spaced relationship relative to the transfer means requires a second, lower current.
Each print engine may include a cleaning station, arranged upstream of the printhead, for cleaning the surface of the transfer roller. The cleaning station may include a cleaning element of an absorbent, resiliently flexible material such as a sponge, and a wiper of a resiliently flexible material arranged downstream of the cleaning element. The wiper may be of rubber.
Each print engine may provide for process color output.
The print engines may be operable substantially simultaneously to effect substantially simultaneous printing on both surfaces of the print media passing between the print engines.